The Gelation Mechanism of an Apple Polysaccharide at Ambient Temperature as Induced by Ca2+

In this study, an apple polysaccharide (AP) that exhibited a gelatin-like gelation behavior has been reported, with the gelation mechanism being further revealed. It was found that a suitable amount of Ca²⁺ addition (4.5 mmol·L^-1) induced the formation of AP gels at 0.5% (<i>w/v</i>) polymer concentration in a wide pH range (3.0-8.0) by holding the polysaccharide solution at 4 °C. However, no gel was formed in the absence of Ca²⁺. Meanwhile, all gels melted around 33 °C upon reheating, and the change in pH did not significantly affect the formation and melting processes of the AP gels. Furthermore, ITC and EPR measurements indicated no detectable binding of Ca²⁺ to AP chains. Thus, the gelation mechanism was explained as Ca²⁺-mediated electrostatic screening, whose presence facilitated AP chain-chain association and ultimately triggered network formation. Our results suggested that AP may exhibit high potential as a possible gelatin substitute in food production.